conceptual systems design (lscits engd 2011)

• LSCITS, Systems Engineering Course, Conceptual Systems Design Slide 1

Conceptual Systems Design

Discusses early design activities in the systems engineering process


Requirements and Design •  For complex computer-based systems there is no clear

boundary between requirements (what the system should do) and design (how the system should do it)

•  In general, a high-level design is developed from an abstract specification and this design then constrains the more detailed specification of the system


Design/specification activities

•  Concept formulation

•  Problem understanding

•  High-level requirements proposals

•  Feasibility study

•  Requirements engineering

•  Architectural design


Process overlaps

Concept formulation

Problem understanding

Requirements proposals

Feasibility study

Architectural design

Requirements engineering


A spiral model of conceptual design

Concept formulation Problem understanding

Requirements Engineering

Architectural design

Review and analysis

• Start

End


Concept formulation

•  The concept for a system of some type is proposed in response to some perceived problem

•  This concept is generally proposed by people who are outside of the systems engineering process e.g. senior management in a company, politicians or civil servants, pressure groups, etc

•  The concept is usually influenced by factors which influence the thinking of these people such as political and economic benefits


The traffic problem

•  Problem –  Road traffic growth is accelerating so that the number of vehicles is

outstripping the road capacity. This is particularly true for motorways

–  Maintenance costs of current motorways is increasing and there is a need to control these costs

•  Some way must be found of both reducing traffic growth and raising revenue

–  One possibility is to increase road travel costs to encourage people and goods to use alternative forms of transport. This would reduce the number of journeys made, pollution and congestion. The money raised can be used for motorway maintenance


Solution concept

•  A road pricing system could be applied to motorways so that a cost per mile (or km) charge is incurred by all motorway users

•  Other solutions have political drawbacks –  Increasing fuel costs mean that non-motorway users subsidise

motorway users.

–  Large subsidies to other forms of transport to encourage alternative use are not allowed because of European rules on competitiveness.

–  Flat-rate increases e.g. of road tax penalises low volume users of the road system.

–  Flat rate charges means that high mileage users are subsidised by low mileage users.


Problem understanding

•  The process of understanding why the problem has arisen and the impact that the proposed concept is likely to have

•  This process should involve, primarily, domain experts rather than systems engineers although some systems engineering input is essential

–  For the road pricing system, it would include transport specialists, statisticians, civil engineers, environmental experts, etc

–  For a packaging system (for example), it would include manufacturing specialists, packaging suppliers, supply managers, etc


Impact assessment

•  To understand the impact of a proposal, we need to look at the underlying causes of the problem

•  Factors contributing to the growth in traffic

–  Increased individual prosperity means more private cars

–  Reduction in subsidies for public transport

–  Development of automated stock control systems and centralised warehouses

–  Transport privatisation leading to reduced quality of service

•  Impact of motorway pricing

–  Remove hidden subsidies for road users

–  Reduce congestion hence shorten journey times

–  Environmentally acceptable

–  Increased cost of goods


High-level requirements definition

•  This process is concerned with eliciting very general high-level requirements (what the system must do) and system constraints (limitations on how this will be done)

•  It will involve senior decision makers and people involved in the management of the processes where the system will be deployed such as senior traffic police, local authorities, etc

•  Requirements at this stage will be vague - they should not exclude particular solutions.


Road pricing system

•  High-level requirements –  The system must provide a facility whereby cars travelling on motorways

pay a fee which is proportional to the distance travelled

–  The fee charged should be settable by the government of the day and may vary from place to place and time to time in the system

•  Constraints –  The system must not introduce additional traffic delays

–  The system must be run without subsidy

–  The system should be run by a non-governmental authority

–  Use of the system should not require modification by a garage of existing vehicles

–  The system should be introduced within 5 years


Feasibility study

•  The objective of a feasibility study is to investigate, in depth, possible ways to implement a road pricing system

•  Stages of a feasibility study include –  Assessment of existing systems

–  Technology assessment

–  Solution proposals

–  Cost/benefit analysis

•  On completion of the feasibility study, a decision is made on a preferred solution


Assessment of existing systems

•  Other systems of the same or similar types which have been introduced elsewhere should be examined and various questions asked:

–  What has been the practical experience of introducing these systems?

–  What problems are there in introducing and operating these systems?

–  What are the differences between the context of these systems and the planned system context?

–  Can all or part of these existing systems be reused?


Technology assessment

•  What kind of hardware might be needed to implement a road pricing system?

–  Is this hardware available commercially?

–  Would special-purpose hardware have to be designed and manufactured?

•  What software would be needed?

–  Are off-the-shelf software solutions available?

–  Can existing hardware/technology meet the performance demands of the system?


Hardware

•  Vehicle presence sensors –  Detect a vehicle in a traffic lane. Must work in all weather conditions

and at night

•  Vehicle identification system

–  Identify individual vehicles with a high level of reliability

–  Must work in all weather conditions and at night

–  Must not be high cost or require permanent fitting to the car

•  Hardware for collecting charges from drivers


Software

•  General purpose database system for payment collection

•  On board, real-time system for managing car identification

•  Real-time charging system

•  Other database systems for identification, exemptions, offender tracking, etc


Design proposals

•  Normally, there are several possible potential system designs that could solve the problem. These will each have their own advantages and disadvantages

•  Various techniques such as brainstorming may be used to develop potential solutions

•  Each possible design proposal should be described in sufficient detail to allow a cost benefit analysis to be carried out


Road pricing system options

•  Toll ‘gates’ on motorway

•  Satellite position reporting

•  Number plate recognition system.

•  Transponder-based identification

•  Centralised periodic billing

•  Direct debits

•  Real-time payments

•  Pre-payment


Satellite tracking

•  The position of each vehicle is continually tracked by a satellite positioning system and the actual motorway usage is computed

•  Advantages –  Needs only simple hardware on slip roads

–  Would allow system to be extended to other types of road at low cost

•  Disadvantages –  Technology is untried on such a large scale

–  Needs new GIS software to determine motorway usage

–  Needs in-car hardware to send position to satellite


Number plate recognition

•  Equipment is installed at each tolling station to record and recognise each car’s number plate

•  Advantages –  No on-board vehicle equipment is needed

–  No need for real-time response from the system

•  Disadvantages –  Cost feedback to driver before payment is impossible.

–  Centralised vehicle registration information is unreliable and incomplete.

–  Can’t deal with vehicles from outside the UK.

–  May have problems operating in bad weather.

–  Loss of privacy for the driver.


In-car transponder

•  Each car broadcasts its registration when it passes a tolling station. This is detected then the driver is billed

•  Advantages –  Cheap and fairly simple on-board equipment

–  No need for real-time response

–  Based on well-tried technology

•  Disadvantages –  Real-time payment is impossible

–  Needs backup system for cars without transmitters


Smart-card system

•  Each vehicle has a pre-paid debit card. When it passes a tolling station, the toll is debited from the card

•  Advantages

–  Pre-payment of road tolls. Fewer billing problems

–  Easier to anonymise - need not be based on car registration

•  Disadvantages

–  Needs real-time response with new technology

–  Needs backup identification system


Cost/benefit analysis

•  Each proposed solution is considered and, based on its advantages and disadvantages, an estimate of the costs of developing that solution and the associated benefits is made

•  Ideally, one solution should have the lowest costs for the greatest benefits and this should be chosen. In practice, however, some more subjective judgement may have to be made

•  Once a decision has been made on solution technology, then the system architecture can be designed


Key points

•  Conceptual systems design is the process of realising a conceptual design for the system that will be the basis for deriving the system requirements and architecture

•  Key activities include

–  Concept formulation and problem understanding

–  High-level requirements proposals

–  Feasibility study

–  Requirements engineering

–  Architectural design

conceptual systems design (lscits engd 2011)

Technology

systems engineering

systems engineering

systems engineering

systems engineers

highlevel design

road system

complex computerbased

architectural design